Method and device for reducing water friction on the hull of a ship

ABSTRACT

The invention relates to a method for reducing water friction on the hull of a ship, particularly a canal boat, in which a gas is introduced between the hull and the surrounding water below the water level. The inventive method is characterized in that the gas is introduced into the water in an upper area of the hull close to the water level and that, when the ship is in motion with a resulting water flow along the hull, the introduced gas is guided aftwards into a lower lying area of the hull, particularly below the ship&#39;s bottom. The invention also relates to a device for reducing water friction on the hull of a ship.

The invention relates to a method for reducing water friction on thehull of a ship, particularly a canal boat, according to the preamble ofclaim 1, in which a gas is delivered below the water level between saidhull and the water surrounding it in at least one delivery area providedon the hull.

The invention also relates to a device for reducing water friction onthe hull of a ship according to the preamble of claim 7, having a meansfor producing a gas flow on the underbody of the said hull, and at leastone delivery area provided on said hull, which is in flow connectionwith the means and which is constructed for delivering gas between thehull and the water surrounding it.

The introduction of gas, particularly air, on the underbody of a shiphull in order to reduce resistance during the movement of the ship as aresult thereof is e.g. known from U.S. Pat. No. 6,145,459. Thisprinciple is also known as air lubrication.

U.S. Pat. No. 6,145,459 teaches the introduction of the gas into thesurrounding water at the ship's bottom and optionally laterally on thehull. Since on introducing the gas the hydrostatic counterpressure ofthe surrounding water must be overcome and to this may be addedresistance provided by ventilating means, in particular the ship'sbottom-side introduction of gas requires a comparatively high gaspressure. Thus, comparatively complicated means are necessary forproducing a gas flow, which can lead to increased energy costs.

The object of the invention is to provide a method and a device withwhich it is possible to effectively reduce in a particularly economicmanner water friction on the hull.

According to the invention the object is achieved by a method having thefeatures of claim 1 and a device having the features of claim 7.Preferred embodiments of the invention are given in the dependentclaims.

The inventive method for reducing water friction on the hull of a shipis characterized in that the gas is introduced into the water in anupper area of the hull, close to the water level, and that the gasintroduced during the movement of the ship is guided with a resultingwater flow aftwards along the hull into a lower lying area of said hulland in particular below the ship's bottom.

A fundamental concept of the invention consists of introducing the gasat least partly into the area just below the line of floatation of theship and in particular bowside, instead of exclusively at the ship'sbottom. The water flow at the bow can be used to transport the gas intothe depth below the ship's bottom. It has been found that the staticcounterpressure to be overcome on introducing the gas can be aparticularly relevant factor for the efficiency of the method,particularly for an optionally necessary gas flow producing means. Thus,in a type of ship investigated in exemplified manner it has been foundthat on introducing the gas directly at the ship's bottom in the case ofa draught of e.g. 360 cm, an electric fan performance of above 150 kWmay be necessary. On introducing the gas directly below the line offloatation said electric fan performance can be reduced to below 40 kW.

The inventive method can fundamentally also be used for the hulls ofoceangoing ships. However, the method is particularly appropriate inconjunction with canal boats, especially shallow-draught boats, i.e.those having a relatively limited draught. With such ship types the hullcan be constructed in a particularly advantageous manner for the waterflow downward transport of the introduced gas.

The gas provided according to the invention can be fundamentally chosenat random. However, a particularly economic method results from the gasbeing air. A delivery area in the sense of the invention can inparticular be such an area on the hull where the gas can be guidedthrough the hull wall from the interior of the hull outwards into thesurrounding water. To this end the hull appropriately has introductionopenings in the delivery area. These introduction openings can e.g. beconstructed as holes in rows. Alternatively or additionally the holescan also be formed in a porous material. Preferably the gas is deliveredin the form of bubbles, particularly microbubbles, between the hull andthe surrounding water.

The upper area of the hull is, according to the invention, in particularunderstood to mean an area which is directly below the line offloatation. Appropriately, starting from the water level, the upper areaextends by max. 1.5 m and preferably 1 m into the deep. The upper areais preferably a bow area of the ship. The lower lying area in which thegas is guided with the water flow is appropriately in the vicinity ofthe ship's bottom.

According to a particularly preferred development of the inventivemethod, the introduced air is guided on a sloping bow into the lowerlying area of the hull. It is particularly advantageous for the slopingbow to be constructed in the form of a horizontal wedge. With such asloping bow shape it is possible to largely prevent the introduced gasfrom flowing out in the water surface direction laterally with respectto the water flow. A stern and connection area with the preferablylargely flat ship's bottom can be connected to the sloping bow.

An advantageous further development of the inventive method comprisesthe introduced gas being guided between two guide elements or catamaranhulls located externally on the hull into the lower lying area of saidhull. Preferably the guide elements are positioned laterally on thewedge-shaped sloping bow. The guide elements e.g. constructed ascatamaran hulls can in particular serve to reduce a lateral outflow ofthe introduced gas in a direction at right angles to the water flow.

According to the invention it is appropriate to introduce the gas intothe water in ship's position-dependent manner and in particulardraught-dependent manner. This can in particular mean that in the caseof a deep-draught ship, i.e. with a high load, the gas is introducedvery high on the hull, whereas with a limited draught it is introducedlow on the hull and close to the ship's bottom. The height of the upperarea on the hull is consequently varied in ship's position-dependentmanner, particularly draught-dependent manner. This makes it possible toensure that the gas is always introduced into the water close to thewater level in draught and position-independent manner. For this purposeit is possible to displace the delivery area and in particular adelivery opening heightwise on the hull. However, it is particularlyadvantageous to determine a geometrical position of the hull,particularly its draught and as a function of the geometrical positionat least one delivery area in the upper region of the hull is freed forthe gas and further delivery areas at a lower hull level are blocked forthe gas. According to this embodiment of the invention there areconsequently several delivery areas at different hull heights. Withrespect to said delivery areas and as a function of the geometricalposition, at least the highest delivery area below the present waterlevel, i.e. that closest to the water line is freed for the gas.Optionally for a particularly effective air bubble lubrication it isadditionally possible to also free lower lying delivery areas. In orderto reduce undesired gas losses, it can be particularly advantageous toblock for the gas delivery areas above the water level.

The concept of the geometrical position as a function of which thedelivery areas are freed or blocked can in particular be understood tomean the draught of the hull. Alternatively or additionally thegeometrical position of the hull can e.g. be characterized by therolling and/or pitching of the hull and corresponding deflection angles.This makes it possible to ensure according to the invention that alsowhen swell occurs the gas is always delivered directly below the waterlevel. To take account of swell, it is alternatively or additionallypossible to have a certain minimum spacing between the freed deliveryarea and the water level when the ship is stationary.

According to the invention a particularly effective air lubrication canbe obtained by introducing the gas into the water in the form of gasbubbles, particularly as a bubble mist.

In order to reduce an undesired enlargement of the gas bubbles whenflowing along the hull, at a predetermined distance from the openeddelivery area it is possible to at least partly take up the gas bubblesfrom the water and then to introduce the gas back into the water with afurther fan mechanism in order in this way to bring about the startingbubble size. The distance can e.g. be between 4 and 6 m. However, thisprocedure can be comparatively energy-intensive. Thus, it isparticularly preferred by the present invention for the gas bubbles areguided and/or structured along a guide layer, particularly with a threadand/or fibrous material. This guide layer can in particular beconstructed in such a way that, whilst largely retaining the bubblesize, the said gas bubbles flow in microbubble form along the guidelayer or on the surface thereof. For this purpose the guide layer can inparticular have fibres and/or threads, whose length is in the range ofthe desired bubble size or also longer. Preferably the fibres and/orthreads also have a colour coating. Structuring in the sense of theinvention more particularly means that the gas bubble size is largelyretained and/or restored. Through the use of a guide layer for guidingand/or structuring the gas bubbles energy costs for the inventive methodcan be further reduced.

The device according to the invention is characterized in that the atleast one delivery area is located in an upper region of the hull closeto a water line thereof on a sloping bow, which when the ship is inmotion is constructed for guiding the delivered gas with the water flowaftwards into a lower lying area of the hull.

The inventive device is particularly suitable for performing theinventive method, so that the advantages referred to in this connectionare obtained.

A fundamental concept of the inventive device is that the at least onedelivery area is not located directly in the lower lying area of thehull, i.e. on the ship's bottom. Instead the at least one delivery areais located close to the water line of the hull, where the gas can beintroduced into the water with a comparatively lower power orperformance of the gas flow producing means. The at least one deliveryarea is so positioned on the sloping bow that when the ship is in motionthe delivered gas is guided with the water flow along the sloping bowinto the lower lying area of the hull and consequently also ensures airlubrication there.

A particularly preferred development of the invention comprises thepositioning of the sloping bow between two guide elements or catamaranhulls positioned externally on the hull. The sloping bow canadvantageously be constructed in the form of a horizontal web, to whichcan be connected aft the advantageously flat ship's bottom.Appropriately the underbody is constructed in the manner described inGerman patent application 103 43 078.

A further preferred development of the invention is characterized inthat there are several delivery areas at different heights on the hulland that between the gas flow producing means and the delivery areasthere is in each case a valve mechanism for gas flow regulation. Thisinventive further development in particular makes it possible to supplyin draught and/or position-dependent manner gas at least to the deliveryarea located in the upper region of the hull directly below the waterlevel. However, lower lying delivery areas and/or delivery areas abovethe water level can be individually blocked for the gas passage by meansof the valve mechanism. This ensures a particularly efficient airlubrication. As a result of the individual regulatability of thedifferent delivery areas by the valve mechanisms, it is only necessaryto have a single gas flow producing means for supplying all the deliveryareas. However, in principle, there can also be several such means,which can be individually controllable.

According to the invention it is also possible to manually operate thevalve mechanisms as a function of the ship's draught. However, it isparticularly advantageous to provide a control device which isoperatively connected to the valve mechanisms for controlling the gasflow as a function of the geometrical position of the hull and inparticular its draught. In particular, the control device canautomatically determine the position of the ship and for this purposethere can also be a determination of the loading weight. As a result ofthe inventive control device a particularly reliable inventive devicecan be obtained.

Another usable development of the invention is characterized in that theat least one delivery area is constructed for the delivery of gas in theform of gas bubbles and in particular in porous manner. The deliveryarea can in particular be flat and have a spray body, which e.g. has aporous plastics material and/or a porous ceramic material.

A particularly appropriate embodiment of the invention comprisesproviding on the underbody of the hull, particularly on the sloping bow,a guide layer, particularly a fibrous layer, for guiding and/orstructuring the gas bubbles. The guide layer can e.g. be embedded in thehull and/or bonded thereto. Appropriately the guide layer has individuallayer strips arranged on the hull at right angles to the direction oftravel. Appropriately the distance between the individual layer stripsis roughly 2 to 8 m, particularly 4 to 6 m.

It is also particularly advantageous for the gas flow producing means tohave at least one fan or blower. The latter is advantageously connectedto the delivery areas by means of a line system located in the interiorof the hull, the valve mechanisms then being positionable on the linesystem.

The invention is described in greater detail hereinafter relative topreferred embodiments and the attached diagrammatic drawings, whereinshow:

FIG. 1A perspective view of the underbody of a hull for performing theinventive method.

FIG. 2 A longitudinal section along A-A of the hull in FIG. 1 with aninventive device for performing the inventive method for differingdraughts.

A hull for implementing the method according to the invention is shownin FIGS. 1 and 2 in the sense of a bow module. The hull is constructedin semi-catamaran manner and has a sloping bow 46, a catamaran hull 41,42 being provided on both the starboard side and the portside thereof.In their bow area the catamaran hulls 41, 42 are constructed in the formof vertical wedges. However, the sloping bow 46 is constructed in theform of a horizontal wedge. The catamaran hulls 41, 42 contain recesses43, 44 for receiving drive means. Starting from the sloping bow 46, therecesses 43, 44 slope aft through the catamaran hulls 41, 42 to theoutside of the hull.

The bow module with sloping bow 46 is provided aft with a box-like sternarea 48 with a substantially flat ship's bottom 49, to which can beconnected one or more, e.g. pontoon-like hull modules. On both the portand starboard sides on stern area 48 and in the extension of thecatamaran hulls 41, 42 are provided guide elements 50, 50′, whichproject downwards from and laterally bound the ship's bottom 49.

An inventive device for performing the inventive method is shown in FIG.2, which is a sectional view along A-A of the hull in FIG. 1 fordifferent draughts t, t′, t″ as a result of a different loading weightof the ship. The water level is in each case indicated by the references10, 10′, 10″, which as a result of the different submergence depth alsocorresponds to the water line on the hull.

The inventive device has a gas flow producing means 36 in the form of afan or blower. Means 36 is connected by means of a line system 37 tothree spatially separated delivery areas 21, 22, 23, which are providedat different hull heights in the wall of the sloping bow 46. Throughsaid delivery areas 21, 22, 23 gas, particularly air, can be introducedinto the water surrounding the hull. For individually regulating the gasflow through the individual delivery areas 21, 22, 23, upstream of eachof the latter is in each case provided in line system 37 a valvemechanism 31, 32, 33.

During the operation of the inventive device the valve mechanisms 31,32, 33 are set in such a way that gas always only passes out of thedelivery area directly below the given water level 10, 10′, 10″. Incontrast, valve mechanisms 32, 33 block the remaining delivery areas,e.g. 22, 23. With the draught t consequently only delivery area 21, atdraught t′ only delivery area 22 and at draught t″ only delivery area 23is freed for the gas flow.

When the ship travels in direction 4, below the sloping bow 46 there isa water flow illustrated by arrows 5 in FIG. 2 for draught t. Said waterflow guides the gas passing out of delivery area 21 in bubble formbetween the catamaran hulls 41, 42 downwards along the sloping bow 46and aftwards below the ship's bottom 49 to stern area 48. A lateraloutflow of the gas at ship's bottom 49 is largely prevented by guideelements 50, 50′.

1-13. (canceled)
 14. A method for reducing water friction on the hull of a ship in which by means of at least one delivery area provided on the hull a gas is delivered below water level in the form of gas bubbles between the said hull and the water surrounding it, wherein the gas is introduced into the water close to water level in an upper area of the hull, from where, when the ship is in motion with a resulting water flow, it is guided between two guide elements or catamaran hulls positioned externally on the hull along the latter aftwards into a lower lying area of the hull.
 15. The method according to claim 14, wherein the introduced gas is guided on a sloping bow into the lower lying area of the hull.
 16. The method according to claim 14, wherein a geometrical position of the hull is determined and as a function of the geometrical position at least one delivery area in the upper region of the hull is freed for the gas and further delivery areas at other hull heights are blocked for the gas.
 17. The method according to claim 16, wherein the geometrical position of the hull is its draught.
 18. The method according to claim 14, wherein the gas is introduced into the water in bubble mist form.
 19. The method according to claim 14, wherein the gas bubbles are guided and/or structured along a guide layer on the underbody of the hull.
 20. The method according to claim 19, wherein the guide layer has a fibrous material or a thread material.
 21. The method according to claim 14, wherein when the ship is in motion with a resulting water flow, the gas is guided between the two guide elements or catamaran hulls positioned externally on the hull along the latter aftwards below the ship's bottom.
 22. The method according to claim 14, wherein the ship is a canal boat.
 23. A device for reducing water friction on the hull of a ship comprising: means for producing a gas flow on the underbody of the hull and at least one delivery area provided on the hull and which is in flow connection with the means and which is constructed for delivering gas between the hull and the surrounding water in the form of gas bubbles, wherein the at least one delivery area is located in an upper area of the hull close to the water line thereof on a sloping bow located between two guide elements or catamaran hulls located externally on the hull, which sloping bow is constructed for guiding the delivered gas when the ship is in motion aftwards with the water flow into a lower lying area of the hull.
 24. The device according to claim 23, wherein there are several delivery areas at different hull heights and between the gas flow producing means and the delivery areas there is in each case a valve mechanism for gas flow regulation.
 25. The device according to claim 24, wherein a control device is provided and is in operative connection with the valve mechanism for controlling the gas flow as a function of a geometrical position of the hull.
 26. The device according to claim 25, wherein the geometrical position of the hull is its draught.
 27. The device according to claim 23, wherein the at least one delivery area is porous.
 28. The device according to claim 23, wherein on the underbody of the hull there is a guide layer for guiding and/or structuring the gas bubbles.
 29. The device according to claim 28, wherein the guide layer is provided on the sloping bow.
 30. The device according to claim 28, wherein the guide layer is a fibrous layer.
 31. The device according to claim 23, wherein the gas flow producing means has at least one fan.
 32. The device according to claim 23, wherein it is designed for performing a method for reducing water friction on the hull of a ship in which by means of at least one delivery area provided on the hull a gas is delivered below water level in the form of gas bubbles between the said hull and the water surrounding it, wherein the gas is introduced into the water close to water level in an upper area of the hull, from where, when the ship is in motion with a resulting water flow, it is guided between two guide elements or catamaran hulls positioned externally on the hull along the latter aftwards into a lower lying area of the hull. 